hdu4346 枚举思维

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http://acm.hdu.edu.cn/showproblem.php?pid=4346

4
?G
RG?
???
????

0
1
1
4

/**
http://blog.csdn.net/julyana_lin/article/details/7849006
*/
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
using namespace std;
typedef long long LL;
const int mod=1000000007;

LL mod_pow(int a,int n,int p)
{
    LL ret=1;
    LL A=a;
    while(n)
    {
        if(n&1)
        {
            ret=(ret*A)%p;
        }
        A=(A*A)%p;
        n>>=1;
    }
    return ret;
}

int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        char a[1005];
        scanf("%s",a);
        int n=strlen(a);
        int unknown=0,r_num=0;
        for(int i=0;i<n;i++)
        {
            if(a[i]=='?')
                unknown++;
            else if(a[i]=='R')
                r_num++;
        }
        LL unbea=(r_num==0);
        for(int i=0;i<n;i++)
        {
            if(a[i]=='R'||a[i]=='?')
            {
                int x=(a[i]=='R');
                unbea=(unbea+(x==r_num))%mod;
                for(int len=1;len+i<n;len+=2)
                {
                    int y=x;
                    for(int j=i+len;j<n;j+=len)
                    {
                        y+=(a[j]=='R');
                        if(a[j]=='G')break;
                        unbea=(unbea+(y==r_num))%mod;
                    }
                }
            }
        }
        printf("%I64d\n",mod_pow(2,unknown,mod)-unbea);
    }
    return 0;
}

hdu4346 枚举思维

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原文地址：http://blog.csdn.net/lvshubao1314/article/details/43602271